A large number of chemicals that are either analogs of adenosine or of adenosylhomocysteine have been examined for their ability to function as inhibitors and/or substrates of adenosylhomocysteinase. The two most interesting compounds studied are 3-deazaadenosine and 3-deazaaristeromycin. Both are inhibitors of adeonsylhomocysteinase but the nature of their inhibitory properties is different in that 3-deazaaristeromycin unlike 3-deazaadenosine is an irreversible or suicidal inhibitor of the enzyme. In vivo both compounds affect the intracellular levels of S-adenosyl-methionine, and andenosylribosyl homocysteine, and inhibit a variety of methylation reactions. Moreover, they exhibit a variety of interesting biological activities such as antiviral activity against a number of RNA and DNA viruses, and are able under certain conditions to prevent cellular transformation induced by pncopgeni viruses. 3-Deazaadenosine, but not 3-deazaaristeromycin inhibits chemotaxis by a mouse macrophage cell line. Ths interesting difference may provide the opportunity to elucidate the biochemical reactions of importance in eukaryote chemotaxis, and can be used as a model for the search and development of other specific inhibitors of transmethylation reactions.